It is often desirable for network connected systems to classify packets within network communications for later processing. Packet classification can use data extracted from data fields associated with the network packets to generate frame classification keys that can be used for later processing associated with the packets. Some packets, however, do not contain certain fields identified for use in data extraction for key generation. As such, default values are often written into the frame classification key for these missing fields when the frame classification key is generated for the packet. After frame classification keys are generated, however, it can be desirable to distinguish between actual data values extracted from the fields associated with the packet data and default data values that were used for missing fields. This task of distinguishing between actual extracted data and default data becomes particularly difficult when identical values can exist for both the extracted data and the default data (e.g., extracted data value can be all logic zeroes and the default value is all logic zeroes).